Late Mississippian glacio-eustasy recorded in the eastern Paleo-Tethys Ocean (South China)

摘要

Long-lived and extensive glaciation during the Carboniferous and early Permian has been the focus of many studies over the past decade revealing systematic changes in sea level and climatic conditions. The nature of the inception of Carboniferous glaciation, however, remains poorly resolved with uncertainty regarding the timing and dynamics of buildup of continental ice sheets. Here we present detailed sedimentary facies and depositional cycles from Upper Mississippian shallow-water platform and contemporaneous carbonate slope successions from the eastern Paleo-Tethys Ocean region (South China) to reveal systematic variations that provide insight into the sedimentary response to the onset of Carboniferous glaciation. Based on detailed sedimentological logging and facies analysis, four upper Visean cycles and four Serpukhovian cycles were identified from the carbonate platform Yashui section, bounded by either subaerial surfaces or zones, or transgressive surfaces. The cycle tops roughly correspond to intervals rich in normally graded bioclastic wacke- to packstones and with distinct rises (similar to 1 parts per thousand) in conodont delta O-18(PO4) in the carbonate slope Naqing section. In particular, the four Serpukhovian cycles correlate well to depositional cycles defined in the Lower Yangtze Platform succession of South China and in the cyclothemic successions in the Donets Basin, Ukraine, suggesting a glacio-eustatic control, most likely caused by repeated advance and retreat of Gondwana glaciation during the onset but prior to widespread glaciation across the mid-Carboniferous boundary.